A host of new technology applications like hotstamping of sheet metal components can help carmakers achieve much better safety performance.
11 Jun 2023 | 10319 Views | By Chandan B Mallik and Manobhava Baruah
Modern cars can be described as technology on wheels when it comes to performance, efficiency and connected features. But making them as per prescribed norms by regulators and safety bodies means that there are times when the process has to factor in conflicting objectives. For instance, regulators want cleaner cars ...
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Modern cars can be described as technology on wheels when it comes to performance, efficiency and connected features. But making them as per prescribed norms by regulators and safety bodies means that there are times when the process has to factor in conflicting objectives. For instance, regulators want cleaner cars and high levels of active and passive safety features while users want all those and more with better miles per gallon and efficiency.
This is where structural engineers and various safety and production technologies come into play. Cars made in India are becoming safer and are now able to meet benchmark global safety standards thanks to the availability of state-of-the-art technologies like hot stamping.
Most sheet metal parts that go into making the body-in-white (BIW) are usually made using cold stamping of various grades of sheet metal. The BIW is created by welding together all of the vehicle’s structural components, minus moving parts, to make a unit construction.
“Of all the elements of safety of the car, the most important is the car body structure, due to the protection that it provides to passengers when a collision takes place,” says Glyn Jones, Country Manager and President, Gestamp India, a Tier I supplier to several OEMs in the country. The company operates three plants in the country and an R&D centre in Pune. It claims that it has helped increase awareness for safety standards that match those of the Global NCAP.
Gestamp India has introduced hot stamping facilities for OEM clients in India and several brands have engaged its services for various products like A-, B- pillars and various other structural components.
Hot stamped sheet metal products have also been used by Tata Motors in models like Tiago, Punch and Mahindra & Mahindra in XUV 700 and Thar models respectively. All these models have received top safety ratings from global NCAP safety tests and the structural integrity has been attributed to good engineering, design and material application.
In anticipation of the forthcoming Bharat NCAP norms since 2008, Gestamp has invested approximately Rs 1,080 crore with an R&D centre that works on reducing the overall weight of the vehicle using the hot stamping technique. “We recently developed our hot stamping footprint in India and have been very successful over the past seven years. Even in Covid-19 times we were actively investing in the region with our future forward strategy. We need to support the safety aspects in cars as India’s safety regulation changes with Bharat NCAP, BS6 and possibly BS7 norms. We are future ready with our technologies,” says Jones.
Gestamp also works with a host of OEMs like Volkswagen, Skoda, Renault, Ford, Tata, FCA (Fiat Chrysler Automobiles) and Nissan in India. Apart from ICE vehicles, there is also interest from EV makers in stamping products.
Hot and cold stamping
For building the structure of cars, these are two primary metal stamping methods — cold stamping and hot stamping. These are applications where raw sheet metal of various gauges can be converted into the various parts of a car. Both formats use similar metal forming procedures but vary in treatment of the metal itself to create the end product. Most of the stamping business was restricted to cold metal operations so far.
Cold stamping
Cold stamping is shaping metal blanks (pre-cuts from rolls) into desired shapes and designs and is used predominantly in the industry by carmakers for various parts like door panels, roofs, bonnets, boots, firewalls among others. The pre-shaped blanks are subjected to intensive pressure by hydraulic or mechanical presses and the dies shape the metal. Various thicknesses of metals can be deep or semi-deep drawn in single or progressive steps depending on the complexity of the design or part to be made. The role of blank shape matters a lot in cold stamping operations as it allows better finish with almost no stretch marks. However, cold stamping has some limitations in the end product.
Hot stamping
As the name suggests, there’s an extra energy intensive step involved in the stamping process while there are similar operational aspects. Direct hot stamping is a sheet metal forming process involving preheating metal blanks before they are die-punched in the heavy-duty presses. The blanks are heated in a special furnace to as high as 900° C and rapidly cooled after the die process is carried out. The metal retains the form and gains in stiffness and its torsional rigidity is also enhanced. The end product then gets trimmed by laser and undergoes a thorough manual inspection for finishes and tolerances.
Hot vs cold stamping
Cold stamping is around 28 percent less expensive than hot stamping due to the energy required to pre-heat the blanks. While there’s much less energy consumption than hot stamping, it results in both lower energy costs and lower CO2 footprint. The flipside is that hot stamping adds an extra dimension to the equation. Depending on the design of the component to be made, the process can shave off 15-30 percent weight without compromising on the strength.
The advantage with hot stamping is that complicated shapes can be made, and the strength or tensile characteristics of the metal can be altered at the molecular level. To make a particular product, both hot and cold stamped parts of various thicknesses can be spot welded together. And this aspect has been fully exploited by structural engineers when designing new cars. Parts like the A-, B-, C-pillars, chassis sections, cross members, structural supports are among parts that are now being fabricated with this specific technology application. In both methods, progressive die stamping of metal sheet strips is possible with continuous ramming, shaping, and cutting.
Gaining popularity
For car makers in India, availability of hot stamping facilities comes as a boon as future cars are subjected to stringent safety norms. As a result, it is the ultimate material properties that the hot stamping process offers that strongly motivates structural engineers to opt for the application despite its cost disadvantages over cold stamping products. Nowadays, engineers are relying more on metal parts from hot stamping processes, so their requirements are challenging. Technically, hot stamped prodcts or parts need to be sturdier and lightweight, as the automotive industry moves forward with lightweighting and efficiency technologies. It has become obvious that such properties improve the fuel economy and help with crashes and accidents since high-strength materials don’t break quickly or perish on impact.
Future prospects
According to Jones, many cars are welding structural parts like the A-, B-, C-pillars. With advanced technologies and hot stamping applications, it will be possible to make all these as a single part in future cars. “Our engineers are working on it,” says Jones.
This feature was first published in Autocar Professional's June 1, 2023 issue.